Antibodies are drawing attention as pharmaceuticals as they are highly stable in blood and have low antigenicity. Among them, agonistic antibodies that recognize cell surface expressing proteins such as receptors and can elicit specific reactions to cells are considered to be useful as pharmaceuticals. Several agonistic antibodies such as those against erythropoietin receptors and those against thrombopoietin receptors (J. Biol. Chem., (1996), 271(40), 24691-24697: Non-patent Document 1) have already been reported.
Furthermore, in recent years, with the objective of antigenicity against human, half-life in blood, and such, altered antibodies produced by subjecting antibodies to some sort of amino acid sequence alteration such as substitution have been developed as pharmaceuticals. For example, there are many reports on chimeric antibodies and humanized antibodies produced by performing humanization, chimerization, and such to reduce antigenicity against human. Such humanized antibodies and chimerized antibodies are considered to have excellent properties as pharmaceuticals. In addition, to improve half-life of antibodies in blood, and such, antibody constant regions produced by altering the amino acids of human-derived antibody constant regions have been reported as well (WO 2009/041613: Patent Document 1).
However, there are no reports of altering amino acids in antibody constant regions to enhance the agonist activity of antibodies.